Reasoning About Action I: A Possible Worlds Approach

Abstract: Reasoning about change is an important aspect of commonsense reasoning and
planning. In this paper we describe an approach to reasoning about change for
rich domains where it is not possible to anticipate all possible problems or
situations that might occur. The approach provides a solution to the frame
problem, and to the related problem that it is not always reasonable to
explicitly specify all of the consequences of actions. The approach involves
keeping a single model of the world that is updated when actions are
performed. The update procedure involves contructing the nearest possible
world to the current one in which the cosequences of the actions under
consideration hold. The way we find the nearest possible world is to
construct all proofs of the negation of the explicit consequences of the
expected action, and to remove a premise in each proof from the current world.
Computationally, this construction procedure appears to be tractable for
worlds like our own where few things tend to change with each action, or where
change is regular.